The aim of this project is to identify environmental samples that have microorganisms present that are capable of transforming and detoxifying common pollutants. After identification of such samples, the optimal conditions, microorganisms, biodegradative pathways, and mechanisms are investigated at the appropriate level. At the microbial community level, microcosm incubations are used to assay the ability of the microflora present in the sample; examination at the cellular level is done through enrichment and isolation of single species or defined microbial consortia; and at the molecular level, genetic probes and enzyme assays are employed. The biodegradation of two classes of compounds are being studied, halogenated aliphatic compounds and aromatic hydrocarbons. These two classes of compounds are very common groundwater and wastewater pollutants. Successful strategies to bioremediate contaminated waters require a thorough understanding of the metabolic role which the pollutant plays in the biodegrading microorganism(s) in order to optimize and predict reaction rates. After aseptic, anaerobic sampling vials. Sterilized controls are run in parallel and gas chromatographic analyses reveal decreases in contaminant concentrations due to biological activity. We are developing toxicity bioassays to complement the chemical analyses to ensure that toxicity reduction is indeed occurring as a result of biodegradation. Specifically, we have sampled contaminated groundwater and wastewater digestors and have documented the biological dechlorination of chloroform, dichloromethane and Freon-11 (trichlorofluoromethane). We have identified methanogenic, denitrifying and sulfate-reducing bacteria to be the anaerobic microbial groups responsible for the respective biodegradation of these three compounds.